The research objectives of this Program are to broadly evaluate mechanisms of arterial pressure regulation in normal and hypertensive states utilizing a variety of experimental and analytical techniques. Emphasis is placed on the control of body fluid volume by the kidney and mechanisms which determine systemic vascular smooth muscle tone. A special emphasis is placed on utilization of computer system analysis techniques to evaluate the complex interactions of cardiovascular function. The title of the specific projects proposed in this application best summarize the research to be performed, as follows: 1. Vasopressin Secretion and Cardiovascular Function. 2. Vasopressin in Essential Hypertension. 3. Direct Influence of Arterial Pressure on Renal Tubular Function. 4. Neural and Endocrine Control of Water and Electrolyte Balance. 5. Neural Control of Renal Function in Unanesthetized Animals. 6. Alteration of Vascular Muscle Tone and Bed Design in Small and Microcirculatory Vessels during Development of Spontaneous and Volume-Expanded Hypertension. 7. Cardiovascular System Integration.